The invention is related to a seal assembly for an internal valve of a downhole oil well tool such as an oil well packer.
Normally, a well packer is used in oil or gas operations to seal one zone above the packer from another zone below the packer within the casing of a well bore. Packers are used for numerous operations such as zone flow testing, cementing, acidizing, and other fracturing operations.
One of the primary requirements of a satisfactory well packer is that it may be placed at a desired location and selectively set into a gripping and sealing engagement across the well casing so it can support fluid pressure from above or below an effectively isolate two zones within the casing string. When a packer is sealed in a casing, one seal is formed between an exterior portion of the packing and an interior portion of the casing and additionally another seal is formed within the packer between a mandrel and an internal valve within the packer. Obviously, the failure of either of the seals can result in fluid leakage between the separated zones within the casing which is basically undesirable. The achievement of a dependable and reliable seal within the packers internal valve has presented a difficulty in the development of well packers.
A typical packer internal valve seal assembly has a seal ring of elastomeric material that is bonded to and molded in place inside a groove in a metal seal carrier. Also, typical seal rings may have a groove formed around a mid-portion of the face seal to divide the seal into two segments
In the normal operation of a packer, fluid flows through a port immediately above the seal assembly, through the valve chamber, past the face of the seal and into the packer body cavity below while the packer is being run into or withdrawn from the well casing. In the setting operation of the packer, the packer body is displaced upward over the mandrel and the valve member on the mandrel engages the face portion of the seal ring. When this occurs, a relatively higher fluid flow rate is experienced by this seal element as the valve member moves toward the seal ring. The high fluid flow rate at this time tends to erode or deteriorate the seal capability of this valve seal rather rapidly. In extreme cases where the fluids contain particulate material and travel at relatively high flow rates, the valve seal can be eroded to the point of leaking after opening and closing the valve only two or three times. Another inherent difficulty with a bonded seal such as described above is retaining the elastomeric seal in the metal carrier ring. This problem is particularly acute for a seal shown in this patent because the dimension of the seal across the bottom of the groove is significantly larger than the depth dimension of the seal within the groove. Therefore, the broad portion of this seal can easily be pulled from the groove when high flow rates are encountered and if there is a failure in the bond or a failure in the seal material, this will allow a portion or possibly all of the seal to be dislodged from the carrier ring. The overall results of failure of a packer internal valve is that leakage can occur between the zones which are desired to be isolated within the well casing, thereby hindering the operation being performed on a particular well. Also, when these seals are damaged, the packer must be disassembled and the valve seal carrier replaced with another unit which is time consuming, troublesome and expensive for oil well field operations.